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Cooling aluminium welds

Im looking for information in regards to the air quality that is needed for cooling aluminium welds after the initial welding process, , bearing in mind that if it is part of a stitch weld then there will be futher welding to take place, so obviousley the air must be free of compressor oil and water vapour, but to what extent. This is information that is needed by a firm who is to install filters on the compressed air lines to remove these impurities. Any ideas

I have never cooled AL welds as they cool pretty fast while heating the whole thing up. Since AL doesn't like anything but AL, I would say clean dry air and you set the parameters of contaminates for the process.

there might be some here that know more about this than me, but i have always been told that you let a weld cool on its own. as for the other, oil has hydrogen in it the same as water(moisture). the one thing that i definately know is that hydrogen readily dissolves itself into molten aluminum, as the metal cools, the hydrogen connot escape, creating hundreds of tiny voids called porosity. with that in mind, if you must cool a piece that is to be welded on some more, no oil, no moisture at all. when i weld aluminum i go to great pains to get the metal as clean and dry as possible, before i even start removing the oxide layer. i use m.e.k. to get rid of the oil, and preheat to 300 to get rid of the moisture, even before that i run the metal through several cleaning stages, like hot caustic soap, rinse, nitric and sulfuric acids to etch, rinse, then clea with m.e.k. or acetone. then brush right before weld

All I can think about is the possibility of welds cracking. Aluminum already cools to fast for it's own good (hence the requirment for filler every time you strike an arc) so I sure as heck don't see artificialy cooling them as a good idea.

Force-Cooling Aluminum? Why?

I've only seen aluminum force-cooled once: it was a case of necessity where a piece of equipment was "down" and that affected potential life-saving capabilities of said piece of equipment.

I have, however, seen welding situations where aluminum was welded in an aluminum "tray" that was immersed in water, so that residual heat dissipated that much more quickly so that the parts could be pulled out of service, repaired (usually hairline cracks) and put back into service in approximately half the time if it was simply allowed to dry on its own with no external influence.

It is my guess---and Aerometalworker, SundownIII, Sundown, Pangea, and/or BlackWolf would have to give you the metallurgical specifics---that depending on which AL alloy you're using, and thereby its silicon and/or magnesium content, would aid in determining the amount of "force-cooling" you'd be able to get away with...again, depending on which variety of AL you were dealing with.

Unlike the ductility of most steels, I think you're going to find that most AL alloys are going to be too brittle during the cooling process for you to force-cool with gas or liquid. Speaking of 'gas' though, there may be a way to force-cool it using Argon or Helium, since He is "colder" than Ar; surrounding the welded joint with excess He or Ar under pressure might dissipate the heat more rapidly than simply leaving it exposed to ambient air. And then again, the process for surrounding said-joint with said-mixture might be more time-consuming than if you simply allowed it to cool "naturally".

One last point, and this touches briefly on what's already been said, is that: ALO^2/3 forms almost immediately during and after a weld...AL's own version of built-in protection from the elements and one reason it's so good at combating the decaying forces of other Elements. If you screw with that process, you might be shooting yourself in the proverbial foot in terms of weakening whatever properties of the AL you were using it for in the first place.

i talked with an old timer locally about this and was told that when you weld aluminum, it becomes annealed. when you cool a weld on AL faster than normal, it can "crystalize" the weld making it brittle, thus weaker than in the annealed state

Thanks for the input

I will be passing these replies around the workshop as there are some good points that have been raised.
As a matter of interest we are tig and mig welding 5083 in the h321 temper with either 5356 wire or 5183 depending on what is spec,ed by the designers covered with argon HP.
We are also about to do tests with Argon Helium mixes of 75/25 and 90/10,
Any futher comments would be appreciated